Plural concentric parabolic antenna for omnidirectional coverage



May 2, 1967 K s. KELLEHER 3,317,912

PLURAL CONCENTRIC PARABOLIC ANTENNA FOR OMNIDIRECTIONAL COVERAGE FiledJuly 29. 1963 .3 Shets-Sheet 1 INVENTOR Kennelh J Xe/leher May 2, 1967K. S. KELLEHER PLUBAL CONCENTRIC PARABOLIC ANTENNA FOR 7 OMNIDIRECTIONALCOVERAGE Filed July 29. 1963 5 Sheets-Shet 2 AGE/VT May 2, 1967 K. s.KELLEHER PLURAL CONCENTRIC PARABOLIC ANTENNA FOR Sheet 5 OMNIDIRECTIONALCOVERAGE 3 Sheets Filed July 29. 1963 PARABOLA INVENTOR fiennef/v J.Kalle/Yer BY AQM/f M AGENT BEAM PATH in? rows United States PatentCfitice 3,317,912 Patented May 2, 1967 3,317,912 PLURAL CONCENTRICPARABULIC ANTENNA FOR ()MNIDIRECTIONAL COVERAGE Kenneth S. Kelleher,Mount Vernon Magisterial District, Va. (1115 Marine Drive, Alexandria,Va. 22307) Filed July 29, 1963. Ser. No. 298,505 Claims. (Cl. 343-836)This invention relates in general to microwave communication systems andin particular to an antenna device for use with multiple communicationlink stations.

This route transmission such as is involved in radio relay ortropospheric relay systems has presented numerous problems and many ofthese problems have yet to be overcome. Generally, it is desirable todevelop thin routes in a number of radial directions at selectedterminal points in cross-country systems. The antenna system chosen toprovide this link between the terminal station and the stations remotetherefrom is often required to have a high gain, that is, a large poweroutput in each significant radial direction is required. Thus, anomnidirectional antenna which widely distributes the power output isimpractical and directive beam means must be employed. Separateparabolic dish reflector antennas for each thin route, which providedirective beams of the order of 3 degrees, are frequently employed asthe directive beam means in such cases and this solution has proven tobe highly satisfactory in applications involving a few thin routes. Itis obvious, however, that as the number of thin routes increases, themanifold compounding of size, weight, wind resistance, cost factors,etc., greatly complicates this solution to the problem. It will beappreciated that a microwave communication system antenna which enablescommunication over an unlimited number of thin routes involving arelatively small, lightweight, low cost structural assembly is neededand would be welcome as a substantial advancement of the art.

Accordingly:

It is an object of this invention to provide an improved multiple pathmicrowave antenna system which permits servicing of an unlimited numberof thin routes.

It is another object of this invention to provide an improved microwaveantenna device wherein the overall size of the structural assembly isnot increased as the number of thin routes to be serviced is increased.

It is also an object of this invention to provide an improved microwaveantenna device wherein the over-all weight of the structural assembly isnot substantially increased as the number of thin routes to be servicedis increased.

It is a further object of this invention to provide an improvedmicrowave antenna device wherein the wind resistance of the structuralassembly is not increased as the number of thin routes to be serviced isincreased.

It is still another object of this invention to provide an improvedmicrowave antenna device wherein an increase in the number of thinroutes to be serviced does not increase the cost factor in directproportion thereto.

It is still another object of this invention to provide an improvedmicrowave antenna device capable of directed beam communication withremote stations in any direction.

It is also an object of this invention to provide an improved microwaveantenna which is readily adaptable to top or side mounting onconventional antenna masts.

It is an additional object of this invention to provide an improvedmicrowave antenna device wherein any number of feed means may be trainedon the reflector assembly.

It is still a further object of this invention to provide an improvedmicrowave antenna device wherein any number of feed means may be trainedon the reflector assembly and the number may be varied withoutsignificant disturbance of the antenna system.

Other objects of this invention will become apparent upon a morecomprehensive understanding of the invention for which reference is hadto the following specification and drawing wherein:

FIGURE 1 is a pictorial showing of one embodiment of the antenna deviceof this invention.

FIGURE 2 is a plan view diagrammatic showing of the embodiment of FIGURE1 in a communication link network.

FIGURE 3 is a diagrammatic showing in perspective of one segment of thereflector assembly in the embodiment of FIGURE 1.

FIGURE 4 is a diagrammatic plan view of the segment of the reflectorassembly shown in FIGURE 3.

FIGURE 5 is a diagrammatic cross-sectional showing of the segment of thereflector assembly shown in FIG- U-RE 3 together with a typical feedmeans therefor.

Briefly, the device of this invention is a microwave beaming devicehaving a 360 degree capability in a selected plane in which amulti-segment single reflector assembly is employed with a plurality ofindividual feed means trained on this single assembly such that theenergy output of each feed means is directed in beam form towards itsrespective target. The antenna is readily adaptable to mast mounting atany level on any basic mast structure.

Referring now to the drawings:

FIGURE 1 depicts one embodiment of the device of this invention by whicha full 360 degree coverage may be obtained utilizing a three segmentreflector assembly. In FIGURE 1, the three reflector segments 11, 12 and13 are shown atop a mast 14 with a plurality of feed means 21, 22 and 23trained on the segment 11 of the multi-segment reflector assembly. Asimple support means 15 is shown in FIGURE 2 which serves to maintainthe reflector segments in a selected physical relation. This type ofsupport means is not critical to the invention, of course, and othertypes such as a ring or a disc could be substituted as desired. It willbe ap preciated that the reflector segments 12 and 13 also have feedmeans associated therewith and trained in like manner to the feed meansassociated with reflector segment 11. The feed means associated withsegments 12 and 13 are not shown in FIGURE 1 due to the drawingperspective but may be clearly seen in the plan view of FIGURE 2.

In accordance with the invention, each of the reflector segments 11, 1-2and 13 are of the parabolic torus variety which, as is well known in theart, may be derived by rotating a portion of a parabola about a lineparallel to the latus rectum. In FIGURE 1, three substantially 180degree parabolic torus segments are employed to provide 360 degreecoverage. It will be appreciated that more than three parabolic torussegments may be employed if desired. A four segment arrangement may bedesirable in a rectangular tower application, for example, wheremechanical mounting requirements may be critical. In such instance, thesegments may be of lesser degree and approximately degrees has beenfound to be suflicient. It will be appreciated that a minimum number ofreflector segments offers numerous advantages and that the three segmentreflector shown in FIGURE 1 is generally preferred.

While only one multi-segment reflector is shown in the embodiment ofFIGURE 1, it is understood that more than one multi-segment reflectorassembly may be employed on the same mast and that in the case of asecond reflector assembly the two may be widely spaced thereon tofunction as relatively independent reflector assemblies or may beclosely spaced in opposite relation with a common or adjacent feed meansarea for various mechanical and/or electrical advantages, if desired.

FIGURE 2 is a plan view showing of the antenna of this invention in anoperative relation with a plurality of remote substations A, B, C, D, E,F, G, H and I. In FIGURE 2, the reflector segment 11 and three feedmeans 21, 22 and 23 associated therewith enable communication withsubstations A, B and C, respectively; the reflector segment 12 and twofeed means 24 and 25 associated therewith enable communication withsubstations D and E, respectively; and the reflector segment 13 and fourfeed means 26, 27 28 and 29 associated therewith enable communicationwith substations F, G, H and 1, respectively. It is understood, ofcourse, that the number of feed means associated with each respectivereflector segment is not critical and that the number of feed means andthe placement thereof may be altered as the application requires withoutsignificant disturbance of the over-all communication system.

As shown in FIGURE 2, the reflector segments 11, 12 and 13 may beadapted to co-adjacent areas by means of beam crossover at variousdistances from the antenna assembly dependent upon direction of theoverlapping beams. Thus, it will be appreciated that the antennaassembly of this invention may be oriented such that selectedsubstations may be serviced by two separate directive beams fromdifferent reflector segmenqsl, if

desired.

While each of the reflector segments and their respective feed means areshown substantially identical in the drawings, and thus the depictedantenna assembly is operative over a single band of frequencies, it iswithin the purview of this disclosure to provide dissimilarities,dimensional or otherwise, between the several reflector segments andfeed means such that respective reflector segments and feed means areoperative over different frequency bands. In the preferred embodimentthe entire assembly is symmetrical and is operative over a single bandof frequencies. However, it is apparent that in selected applications itmay be desirable to communicate with selected substations utilizing morethan one frequency and that in such instance this may be accomplished byproper asymmetrical design and orientation of the antenna of the presentinvention.

The operation and structure, of the antenna of this invention, may bebest understood by consideration of a single beam path. As described inconjunction with FIGURE 2, each beam path is the product of a singlereflector segment and one respective feed means. FIG- URES 3, 4 anddepict a single reflector segment which is indicative of selecteddimensional criteria.

As mentioned previously, each reflector segment surface is generated byrotating an arc of a parabola about a line parallel to the latus rectum.In the general case, the feed horn is positioned at the focal point ofthe parabola. As shown in FIGURES 3 and 5, one-half of the paraboliccurve may be used and this half may be shortened at either top or bottomif desired to prevent reflected radiations from striking the feed systemin one case and for other purposes.

Since the surface, as defined, is formed by rotating the are about theline ZZ in FIGURE 3, no change in performance is observable as the feedis rotated about the line ZZ. Then, ideally, a plane wave front at anyone feed position should dictate the same characteristic at otherpositions. It is Well known, however, that a paraboloid is required forconversion of a spherical wave into a true plane wave and thus thecurvature of the present invention merely affords an approximation of aplane wave. It has been found that a proper choice of the values forfocal length 1 and for the reflector radius R (FIGURE 3) will yield asurface which has a nearly plane reflected wave front.

In analysis of the reflector surface in terms of the various parameters,it is necessary to determine how closely the reflected wave frontapproaches the desired plane wave. It can be shown that the deviation ofthe wave front from a plane is given by:

(lf) cos 0 Where 0, z and f are as indicated in FIGURE 3.

It is apparent from this equation that the deviation is zero in theplane defined by 6:0. The function A can also be made to vanish byvarious combinations of J and z which would make the expression in thebrackets zero.

It has been found, however, since A(f,z) changes rapidly in theneighborhood of such points, that there is no great advantage in basingan analysis upon the vanishing of the bracketed expression.

An analysis has been made by selecting values of f(R =l) and computingthe function A for various values of 0 and z. It has been found that af/R ratio between 0.4 and 0.5 gives the smallest values of A.

In practical application, it has been found that a symmetrical reflectorshould have an f/R ratio of about 0.45 since for such a case thedeviation in the center of the reflector (z, FIGURE 3) is small. If anasymmetrical reflector is to be employed (from 2:0 to z=0.8, forexample), the f/R ratio should be 0.43 since the deviation is then smallin the region z=0.4. Of course, the optimum values can best bedetermined in each particular system on the basis of radiation patterns.

With the f/R ratio established, other parameters can be considered. Ithas been found that a change in R produces a scaling of the entiresystem and thus yields an increase or decrease in antenna beamwidth.When R (and, therefore, 1) are fixed, the maximum desirable values of zand 0 can be considered. The coordinate z can be increased up to thepoint at which the parabolic arc intersects the axis of revolution ZZbut, in practice, an increase in phase error with increase in z sets themaximum value.

The angle of rotation, 0, can be increased up to the point at which thesurface begins to intercept reflected rays. Thus, if 45 degreepolarization and 45 degree reflector elements were used, 0 could beincreased to 360 degrees. It is appreciated, however, that aconventional feed horn will not, in general, illuminate the entiresurface, but only a portion thereof, for example, 0=+49 and 0=-49.Outside of this region of illumination it has been noted, the phaseerror increases rapidly.

It has been determined that the parabolic torus configuration is vastlysuperior to other configurations for the reflector of this antenna. Forexample, for small values of 0, the parabolic torus has small deviationsapproximating A=O for 6:0. Thus the parabolic torus is inherentlysuperior to the sphere, which has zero deviation in the center and inlimited regions elsewhere.

The antenna of this invention has been compared with the many parabolicdish antennas which it supersedes in the thin route application. Forgain factors less than 35 db, for example, the antenna of this inventionhas been found to equal the parabolic dish antenna in patternefficiency. For higher gains, a slightly larger reflector area has beenfound to be desirable.

FIGURE 4 is a plan view of one segment of the reflector in the device ofthis invention which shows a typical illumination of the reflector. Itwill be appreciated that the angular designations are arbitrarily chosenfor purposes of illustration and that this invention is not restrictedto feed means having such an illumination characteristic. Further, theradius R in each of the FIG- URES 3, 4 and 5 is merely for purposes ofreference and is in no way controlling in the design of the antennarefleet-or segments. As pointed out previously, the parabolic are whichforms the parabolic torus can be shortened at either end as desired,within practical limits.

FIGURE 5 is a cross-sectional view of one segment of the reflectorwherein the relation of the point of feed to the reflector surface isillustrated in greater detail. In FIGURE 5, the feed means iseffectively below the reflector surface and out of the beam path. As aconsequence, the number of feed means, the placement thereof andselected focal points, and the alteration of number and placement offeed means do not alter the radiation characteristics of the antenna.

A practical embodiment of the antenna of this invention with a f/R ratioof "0.46 and with an angle extent of 180 degrees for an f/D ratio of theparabola equivalent to 0.4 which is intended to replace a plurality ofsix-foot diameter parabolic dishes (D-6) might have an f dimension of2.4 feet and an R dimension of 5.22 feet.

It is understood that the exemplary embodiment of FIGURE 1 is merelyillustrative of the invention and that various modifications inaccordance with standard practice in the art are within the purview ofthis disclosure. For example, other truncation of the parabolic torussegments or no truncation of the reflector segments is to be anticipatedin selected applications for various reasons peculiar to theseapplications. Also, the axis of rotation of the several reflectorsegments may be parallel to the center line of the reflector assembly,as shown, or alternatively, at any selected angle relative thereto andthis relation to the center line may be adjustable, by means not shown,for more versatile application of the device.

Likewise, it is not essential that the parabolic curvature be asillustrated and a greater or lesser degree of curvature is permissible.

Further various support techniques may be employed to position thereflector segments in their respective relation. Indeed, the reflectorsegments may be formed as a unitary structure of whatever material isappropriate including nonreflective material, if desired, provided, ofcourse, suitable provision is made for reflective parabolic torussurfaces.

In addition, this invention is not restricted to any particular type offeed means and any presently existing or subsequently developed feedmeans which may be adapted to serve the purposes of the antenna of thisinvention may be substituted. Moreover, the antenna of this inventionmay be employed to beam microwave energy having polarizationcharacteristics other than as indicated, if desired.

Finally, it is understood that this invention is only to be limited bythe scope of the claims appended hereto.

What is claimed is:

1. An omnidirectional microwave antenna having a relatively high gaincharacteristic in predetermined radial directions about a selectedcenter line and adapted for use in thin route communication systemscomprising a reflector assembly having a plurality of N wave energyreflective surface segments, each of said segments having a reflectivesurface configuration of the parabolic torus variety with respectiveaxis of rotation, said axis of rotation being substantially equidisposedwith respect to each other about said selected center line, each of saidsegments disposed with its respective reflective surface facing outwardrelative to said selected center line; and a plurality of wave energyfeed means disposed to direct wave energy at each of said respective Nwave energy reflective surface segments of said reflector assembly suchthat wave energy may be reflected therefrom in predetermined directions,said wave energy feed means being disposed in a common plane and beingspaced equidistantly from the respective reflective surface segmentstoward which Wave energy is directed.

2. A microwave antenna as defined in claim 2 wherein said respectiveaxis of rotation of each of said reflective surface segments are inparallel relation with said selected center line.

3. A microwave antenna as defined in claim 1 wherein said reflectorassembly has a plurality of three wave energy reflective surfacesegments.

4. A microwave antenna as defined in claim 2 wherein said reflectorassembly has a plurality of three wave energy reflective surfacesegments.

5. A microwave antenna as defined in claim 3 wherein each of saidreflective surface segments substantially extend an arc of between anddegrees in the circular plane thereof.

6. A microwave antenna as defined in claim 4 wherein each of saidreflective surface segments substantially extend an arc of bet-ween 120and 180 degrees in the circular plane thereof.

7. A microwave antenna as defined in claim 3 wherein each of saidreflective surface segments substantially extend an arc of approximately180 degrees in the circular plane thereof.

8. A microwave antenna as defined in claim 4 wherein each of saidreflective surface segments substantially extend an arc of approximately180 degrees in the circular plane thereof.

9. A microwave antenna as defined in claim 2 wherein said feed means aresubstantially disposed in a common plane and said selected center lineis in perpendicular relation to said common plane.

10. A microwave antenna as defined in claim 3 wherein said threereflective surface segments of said reflector assembly are substantiallyidentical and said feed means are substantially disposed in a commonplane, substantially equidistant said surface.

References Cited by the Examiner UNITED STATES PATENTS 1,939,345 12/1933Gerth et al 343-836 2,540,518 2/1951 Gluyas 343-840 X 2,955,288 10/ 1960Palmer 343779 2,989,747 6/1961 Atchison 343--779 3,011,167 11/ 196 1Alford 343-83 6 3,016,531 1/1962 T-omiyasu et a1 343779 FOREIGN PATENTS818,131 6/1937 France.

ELI LIEBERMAN, Primary Examiner. HERMAN KARL SAALBACH, Examiner.

1. AN OMNIDIRECTIONAL MICROWAVE ANTENNA HAVING A RELATIVELY HIGH GAINCHARACTERISTIC IN PREDETERMINED RADIAL DIRECTIONS ABOUT A SELECTEDCENTER LINE AND ADAPTED FOR USE IN THIN ROUTE COMMUNICATION SYSTEMSCOMPRISING A REFLECTOR ASSEMBLY HAVING A PLURALITY OF N WAVE ENERGYREFLECTIVE SURFACE SEGMENTS, EACH OF SAID SEGMENTS HAVING A REFLECTIVESURFACE CONFIGURATION OF THE PARABOLIC TORUS VARIETY WITH RESPECTIVEAXIS OF ROTATION, SAID AXIS OF ROTATION BEING SUBSTANTIALLY EQUIDISPOSEDWITH RESPECT TO EACH OTHER ABOUT SAID SELECTED CENTER LINE, EACH OF SAIDSEGMENTS DISPOSED WITH ITS RESPECTIVE REFLECTIVE SURFACE FACING OUTWARDRELATIVE TO SAID SELECTED CENTER LINE; AND A PLURALITY OF WAVE ENERGYFEED MEANS DISPOSED TO DIRECT WAVE ENERGY AT EACH OF SAID RESPECTIVE NWAVE ENERGY REFLECTIVE SURFACE SEGMENTS OF SAID REFLECTOR ASSEMBLY SUCHTHAT WAVE ENERGY MAY BE REFLECTED THEREFROM IN PREDETERMINED DIRECTIONS,SAID WAVE ENERGY FEED MEANS BEING DISPOSED IN A COMMON PLANE AND BEINGSPACED EQUIDISTANTLY FROM THE RESPECTIVE REFLECTIVE SURFACE SEGMENTSTOWARD WHICH WAVE ENERGY IS DIRECTED.